Wildlife Afield 8(1):120-122, 2011 © Biodiversity Centre for Wildlife Studies

Cooper’s Hawk Feeding on Barred Owl and Norway Rat in Victoria, British Columbia

David Stirling

3500 Salsbury Way, Victoria, British Columbia, Canada V8P 3K8

Direct observations of interactions between season (see Roth and Lima 2003). predator and prey, while in the field, are of importance In autumn 2010 and spring 2011, I witnessed in providing new information on a species’ behaviour two interactions between Cooper’s Hawk and Barred as well as contributing to its diet profile. Knowledge Owl in my backyard in Victoria, British Columbia. of the diet of Cooper’s Hawk (Accipiter cooperii; The property includes remnant Garry oak (Quercus Figure 2) and Barred Owl (Strix varia; Figure 1) in garryana) woodland. I maintain bird feeders from North America has been derived primarily from prey autumn to spring during which time Cooper’s Hawk is remains and regurgitated pellets collected at nest and an infrequent visitor and the Barred Owl occasionally roost sites during the breeding period (Rosenfield roosts daily in large ornamental trees in my yard. and Bielefeldt 1993, Mazur and James 2000). Little is Two interactions, both involving food items, known of prey taken during the species’ non-breeding were recorded.

Figure 1. Cooper’s Hawk is one of the growing number of raptors that has adapted well to urban environments. Photo by Mark Nyhof, Ladner, BC, February 1994.

8:1 June 2011 120 Barred Owl (Strix varia) Norway Rat (Rattus norvegicus)

On 1 March 2011, while returning home about At 0830 hr, on 6 October 2010, I saw a Cooper’s 1440 hr, I noticed a large bird of prey, later identified Hawk on top, but struggling with, a live Norway Rat as a female Cooper’s Hawk, holding something in (Figure 3) at the base of a Garry Oak on my back its talons on a branch of a Garry oak near my bird lawn. During the tussle, the rat managed to tip the feeder. The hawk momentarily dropped its prey but hawk onto one wing several times. Eventually the picked it up again and flew to a branch about 1 m from hawk triumphed and flew, carrying the rat, to an the ground. The hawk held the entire Barred Owl exposed limb on an ornamental cedar of Lebanon by its neck. About five minutes later, the Cooper’s (Cedrus libani). A Barred Owl flew out from its Hawk started to pluck the owl, a well-known feeding roost in a nearby large ornamental Monterey cypress behaviour of accipiters (Rosenfield and Bielefeldt (Cupressus macrocarpa) directly at the hawk, but 1993). I decided to get my camera from the house the hawk flew off with the rat when the owl was but the hawk noticed the movement and flew off, almost upon it. carrying the owl barely above the ground, towards a neighbour’s yard, 30 m away and disappeared. I (Stirling 2011) provided a more personal account of this feeding event. This observation appears to represent an act of predation by Cooper’s Hawk on a Barred Owl, but because the capture and killing of the owl were not observed, scavenging cannot be firmly ruled out.

Figure 3. Norway Rat, a common urban mammal on southern Vancouver Island, is nearly four times the average weight usually taken as prey by Cooper’s Hawk. Photo by R. Wayne Campbell, Victoria, BC, 14 March 2008.

It appears that Barred Owl and Norway Rat are new prey species for Cooper’s Hawk. Barred Owl must be near the upper limit of prey that a Cooper’s Hawk can successfully carry. Most prey items reported in the summer diet of Cooper’s Hawk are medium- sized birds and mammals ranging from 50 to 130 g or between 8% and 22% of the body weight of an adult female (Storer 1966, Rosenfield and Bielefeldt 1993). The mass of Barred Owl, both sexes combined, ranges between 468 and 1,051 g more than the mean Figure 2. Barred Owl is now a potential prey species weight of 416 g reported for an adult female Cooper’s for Cooper’s Hawk wherever they co-occur in British Hawk (Earhart and Johnson 1970). Rosenfield (1998) Columbia. Photo by Mark Nyhof, Victoria, BC, 27 reported Cotton Rat (Sigmodon spp.) as a prey item May 2010. but did not list other rodents.

121 Wildlife Afield Cooper’s Hawk and Barred Owl appear to co- Union. 24 pp. exist in mixed forests in urban habitats on southern Roth, T.C. and S.L. Lima. 2003. Hunting Vancouver Island mainly due to differences in behavior and diet of Cooper’s Hawk: An urban hunting times (e.g., diurnal versus nocturnal), nest view of the small-bird-in-winter- paradigm. Condor site selection (e.g., platform versus cavity), food 105:474-483. habits (e.g., mainly small to medium-sized birds Stirling, D. 1970. A sight record of the Barred versus mainly small mammals), and residency (e.g., Owl on Vancouver Island. Murrelet 51:19. partial migrant versus non-migratory) (Campbell et . 2011. A note on the ignominious demise al. 1990, Rosenfield and Bielefeldt 1993, Mazur and of my Barred Owl. Victoria Naturalist 67:6. James 2000). Storer, R.W. 1966. Sexual dimorphism and The Barred Owl was first reported in Victoria, food habits of three North American accipiters. Auk on southern Vancouver Island, on 26 November 1969 83:423-436. (Stirling 1970) and during the following two decades expanded its range to include the entire east side of the island (Campbell et al. 1990). As woodland habitats become utilized, competition between Cooper’s Hawk and Barred Owl may be reported more frequently, especially in urban areas where bird feeders attract a variety of potential prey species.

Acknowledgements I am grateful to Wayne Campbell for help in researching and preparing this natural history note.

Literature Cited Campbell, R.W., N.K. Dawe, I. McTaggart- Cowan, J.M. Cooper, G.W. Kaiser, and M.C.E. McNall. 1990. The birds of British Columbia: Volume 2 - nonpasserines (diurnal birds of prey through woodpeckers). Royal British Columbia Museum, About the Author Victoria, BC. 636 pp. Dave spent his early years on a pioneer farm at Earhart, C.M. and N.K. Johnson. 1970. Size the edge of the boreal forest near Athabasca, Alberta. dimorphism and food habitats of North American He was already a keen observer of the natural world by owls. Condor 72:251-264. the age of twelve. Dave enjoyed observing woodland Mazur, K.M. and P.C. James. 2000. Barred passerines high in the forest canopy while sitting Owl (Strix varia). In The birds of North America, No. quietly and watching frogs and whirligig beetles 508. (A. Poole and F. Gill, eds.). The Birds of North from a stump in a spring pond. He learned early America, Inc., Philadelphia, PA. 20 pp. that by watching chickens with heads aslant and one Rosenfield, R.N. 1988. Cooper’s Hawk. Pages eye pointing skyward that he could locate migrating 353-354 in Handbook of North American birds, raptors. volume 4, part 1: Diurnal raptors. (R.S. Palmer, ed.). Dave graduated as first lieutenant from Sandhurst Yale University Press, CT. Military College, England and later moved to Canada Rosenfield, R.N. and J. Bielefeldt. 1993. where he worked in fisheries and forestry. He finished Cooper’s Hawk (Accipiter cooperii). In The birds of his career with the interpretation and research division North America, No. 75 (A. Poole and F. Gill, eds.). of the British Columbia Parks Branch. Philadelphia: The Academy of Natural Sciences; Dave helped organize and lead over 60 nature Washington, DC.: The American Ornithologists’ tours worldwide. This year (2011) he is 91 years old.

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